Coal preparation accessory



April 10, 1956 H, GLUE 2,741,367

COAL PREPARATION ACCESSORY Filed Sept. 8, 1953 co N Ln INVENTOR.

PERCY H.G|LL|E V ATTORNEY.

United States COAL PREPARA'EEON ACCESSORY PercyHency Gihie, Bluefieid, W. Va, assignor to Allied Chemical & Dye Corporation, New YorlgN. .Y., a corporation of-Nevv York Application September 8, 1953, "Serial No. "378,911

3 Claims. (Cl. 299-441) invention relates to cleaning fine coal and is particularly directed to an improvement in concentrator tables for cleaning fine coal, i. e. separating impurities such as shale, pyrite's, and bone coal from coal. v Conventional practice in cleaning coal is to subject fine 'coal of about inch mesh "to vibrating action in the nature of a reciprocating or oscillating action on a table having 'riflfl'es and simultaneously washing the coal on the table with water. The construction and operation of these tables, termed concentrating tables, "are well known in the art and fully described in the bo'ohilhe -C1eaning of Coal by W. R. Chapman "and 'R. A. Mott, pages 299-526, published by Chapman 8: Hall Ltd. X1923), and the book CoalPreparation, pages 435 469, -tui'blished by The American institute of 'Mining "and Metallurgical Engineers (1950). Concentrating tables usually consist of a rectangular deck with riflles on the top surface of the neck. A drivingcmechanism imparts reciprocating "motion to the deck. Coal feed is supplied at one corner of the deck and refuse discharged at the narrow end of the 'deck remote from the feed. Clean coal is discharged along the longer side of .the deck remote from the feed. Middlings, 'a mixture of coal and refuse, discharge from thelong side of the deck near the corner 'between'the coal discharge side and the refuse discharge end. 'Washing water is introduced along the longer side of the deck opposite the coal discharge 'side. Usually the decks are inclined downwardly toward'the coal discharge side and also upwardly toward the refuse discharge end. The vibratory action of the table and water washing thereo'n cause separation o'f-coal impurities s'udh as bone coal, shale and pyrites from the-low ash coal. Unfortunately, a considerable percentage of unde'sirable bone coal discharged with-clean coal :at Ia'point between the discharging section of the clean coal and the discharging section of the impurities. This intermediate fraction of coal from the table, referred to as middlings, consists primarily of large size bone coal, undesirable fine particles of high specific gravity and desirable fine low ash coal particles. Sometimes the middlings are subjected to a second expensive treatment in an attempt to recover some of the low ash coal but more often the middlings are utilized Without further treatment as an inferior fuel of low value.

One object of the present invention is to provide an improved concentrator table for elfecting more eificient separation of impurities from coal.

A further object of the invention is to provide means for separating middlings in a concentrating table into clean coal and refuse.

Other objects and advantages of the present invention will be apparent from the following description and accompanying drawing.

In accordance with the present invention more efi'icient cleaning of coal with separation of greater yields of clean coal with lower ash content may be accomplished by attaching a vertical, upwardly extending screen, preferably a inch screen, to the longer clean coal discharge side 2,741,367 Patented Apr. 10, I956 add 2 of the table at the 'sec'tion'where the niiddlings discharge, preferably "along the clean coal discharge side of the table extending from about the corner of the table which is diagonally opposite the coal feed corner for a distance of about one-fourth the length of the longer side.

.The'ac'companying drawing is an isometric view of the deck of a concentrating table equipped with the-upright screen.

A typical concentrating table having 'riffies thereon, generally indicated by the numeral 1, is illustrated in the attached drawing. Coal enters through feed box 2 and streams of water are continuously introduced at points 3 and 4. Clean coal moves along the table and discharges from the side of the table lettered A. The refuse, bone coal, shale 'and pyrites, discharges from end B. Middlings "(in the absence of the screen) discharge from the far side o'fthe coal discharge side of the table designated by letter C.

In the operation of concentrating tables it was noted that a considerable percentage of large size undesirable bone coal discharged with clean coal from section C of the table. The clean coal discharging at C is of relatively fine particle size below /4 inch, whereas the impurities, the bone coal, collecting for some unknown reason at that point, are greater than A inch size. In addition high specific gravity undesirable fine particles also discharged at section C. By attaching a vertical screen 5 to the table at section C the large size .bone coal f is prevented from discharging with the clean, .finer coal which passes through :screen 5. Due to the vibrating action of the table, the large size bone coal-trapped by the screen moves onwardly and discharges from table end B withthe other impurities. In commercial practice, a A; inch screen extending upwardly about 4 inches to a height of about 4 inches from the table andfhav ing a length of about 4 feet on a table having a total coal discharge length of about '16 feet was found to give satisfactory results; of course, the sizes may be varied some what, depending upon the nature of the material to 'be treated and type and operation of the table. 'The screen need not necessarily be set at the very edge of the table but may 'be disposed a short distance from the edge. Also, more than one vertical screen may be employed on the table.

It-isimportant to place the screen in an upright vertical position in contrast to a'fia't or Linclined screen to separate large bone coal from fine coal. On the flat or inclined screen the separating force isrmerely gravity and the effect is solely a sizing separation. With the upright screen the particles are moved by a water current actuated by a very small component of gravity. The motion of the particle through the screen is opposed by the motion of the table and the effect of the rifiles on both the particles and the water. The rifiies tend to hold back low specific gravity fine particles as well as high specific gravity large particles. As a result of these opposing forces, undesirable particles of high specific gravity will not have as much tendency to go through the screen as desirable particles of low specific gravity which are more influenced by the current of water. The constriction of the path of particles offered by the screen and the crowding of particles at the screen causes high specific gravity particles to fall out of the transverse water current and be removed to refuse by the motion of the table. Hence, the screen effects a separation according to both size and specific gravity that is not possible on a flat screen. In brief, the upright vertical screen effects separation of middlings composed of undesirable large bone coal, undesirable fine particles of high specific gravity and desirable fine particles of coal of low specific gravity causing the bone coal and high specific gravity fine particles to discharge with the refuse from the end of the table and fine particles of coal to discharge with the clean coal from the side of the table;

Although the attachment of a screen to a concentrating table has been described with particular reference to cleaning coal, the screen attachment is also useful in the separation 01 other solid materials such as ore and mixtures of solids of different sizes and specific gravities.

For purposes of illustrating the present invention and the advantages attendant thereto, two similar operations for cleaning coal were carried out on a concentrating table known commercially as a Deister concentrator table, as illustrated in the drawing, under the same conditions except that in one operation a A1, inch vertical upright screen 3 feet, 8 inches long and 4 inches high was attached to the coal discharge side at its far end. The pertinent results fromthese two operations, namely screen analysis, ash content, and recovery of the feed coal, clean coal and refuse, are tabulated below.

Clean Coal Refuse Feed Table Table Table Table 595 1%;? Without With Without With Screen, Screen, Screen, Screen, Percent Percent Percent Percent Wgt. Wgt. Wgt. Wgt.

Ash Content 17 3O 6. 70 6. 63 51 .57 66 44 Recovery percent 76. 3 82, 2

From the foregoing data it will be noted that recovery of clean coal in the concentrating table operation employing the screen was 82.2% as compared to 76.3% when operating the table without a screen, and furthermore that the ash content of the clean coal recovered in the former operation was lower than the latter. This increase is of real moment when one considers that hundreds of tons of coal are treated daily. 7 Further, the cost of the screen is almost negligible and, of great importance, there is no increase in the cost of operating the concentrating table.

Although certain preferred embodiments of the inven-' tion have been disclosed for purpose of illustration it will be evident that various changes and modifications may be made therein Without departing from the scope and spirit of the invention.

I claim:

1. In a wet concentrating table adapted for separating solids of different specific gravity comprising an imperforate deck adapted to be reciprocated with rifiles on the top surface of the deck, a solids feed inlet to the deck, a liquid feed inlet to the deck, said deck having one side for the discharge of separated lower specific I gravity solids, one end for discharge of higher specific gravity solids, and a section intermediate said discharge sections for the discharge of middlings, the improvement which comprises a vertical screen extending upwardly from the deck at the section where therniddlings discharge to permit passage through the vertical screen of the smaller size solid particles and prevent discharge of the larger size solid particles.

2. In a wet concentrating table adapted for cleaning coal comprising a rectangular imperforate deck adapted to be rcciprocatcd with rifiles on the top surface of the deck, a coal feed inlet at one corner of the deck, a water feed inlet near one long side of the deck, a clean coal discharge section along the opposite long side of the deck, a refuse discharge section along the end of the deck remote from the coal feed inlet, and a middlings discharge section along the long side of the deck between the coal discharge side and the refuse discharge end, the improvement which comprises a vertical screen extending upwardly from the deck at the section Where the middlings discharge to permit passage through the screen of the finer coal and prevent discharge of the large size bone coal.

3. In a wet concentrating table adapted for cleaning coal comprising a rectangular imperforate deck adapted to be reciprocated with rifiles on the top surface of the deck, a coal feed inlet at one corner of the deck, a' water feed inlet near one long side of the deck, a clean coal discharge section along the opposite long side of the deck, a refuse discharge section along the end of the deck remotefrom the feed inlet, and a middlings discharge section along the long side of the deck near the corner between the coal discharge side and the refuse discharge end, the improvement which comprises a vertical screen about A inch size extending upwardly from the deck and extending along the side of the deck from about the corner diagonally opposite the coal feed corner for a distance of about one-fourth the length of the side to permit passage through the screen of the finer coal and prevent discharge of the large size bone coal.

References Cited in the file of this patent UNITED STATES PATENTS wi v 

1. IN A WET CONCENTRATING TABLE ADAPTED FOR SEPARATING SOLIDS OF DIFFERENT SPECIFIC GRAVITY COMPRISING AN IMPEROFRATE DECK ADAPTED TO BE RECIPROCATED WITH RIFFLES ON THE TOP SURFACE OF THE DECK, A SOLIDS FEED INLET TO THE DECK, A LIQUID FEED INLET TO THE DECK, SAID DECK HAVING ONE SIDE FOR THE DISCHARGE OF SEPARATED LOWER SPECIFIC GRAVITY SOLIDS, ONE END FOR DISCHARGE OF HIGHER SPECIFIC GRAVITY SOLIDS, AND A SECTION INTERMEDIATE SAID DISCHARGE SECTIONS FOR THE DISCHARGE OF MIDDLINGS, THE IMPROVEMENT WHICH COMPRISES A VERTICAL SCREEN EXTENDING UPWARDLY FROM THE DECK AT THE SECTION WHERE THE MIDDLINGS DISCHARGE TO PERMIT PASSAGE THROUGH THE VERTICAL SCREEN OF THE SMALLER SIZE SOLID PARTICLES AND PREVENT DISCHARGE OF THE LARGER SIZE SOLID PARTICLES. 